To determine the prevalence of precursor lesions of oesophageal cancer in Linxian, People's Republic of China, which has an extremely high incidence of oesophageal cancer, 527 subjects were interviewed by a questionnaire about exposure to suspected risk factors. They also underwent oesophagoscopy, cytology, and biopsy. 84% had a chronic oesophagitis which had similar endoscopic and histological characteristics to that reported in Iran. The oesophagitis was accompanied by atrophy of the epithelium in 10% of these subjects and by dysplasia in 8%. Re-examination of 20 selected subjects 1 year later showed progression of the oesophagitis to atrophy and dysplasia in 4 individuals and to cancer in 4 others. The surveys in Iran and China suggest that the natural history of oesophageal cancer starts with an oesophagitis which, in a few individuals, progresses to atrophy and dysplasia of the epithelium and finally to cancer. Thermal injury resulting from the drinking of very hot beverages, physical injury caused by ingesting very coarse food, and deficiencies of riboflavine, vitamin A, and zinc are proposed as risk factors for these precursor lesions.